The present invention relates to improved apparatus and methods for performing qualitative and quantitative analysis of microscopic biological specimens. In particular, the invention relates to such apparatus and methods for isolating, collecting, immobilizing, and/or analyzing microscopic biological specimens or substances which are susceptible to immunospecific or non-specific binding with magnetic-responsive particles having a binding agent for producing magnetically-labeled species within a fluid medium. As used herein, terms such as “target entity” shall refer to such biological specimens or substances of investigational interest which are susceptible to such magnetic labeling.
U.S. Pat. No. 5,985,853 describes an apparatus and method wherein an external magnetic gradient is employed to attract magnetically labeled target entities present in a collection chamber to one of its surfaces, and where an internal magnetic gradient is employed to obtain precise alignment of those entities on that surface. The movement of magnetically labeled biological entities to the collection surface is obtained by applying a vertical magnetic gradient to move the magnetically labeled biological entities to the collection surface. The collection surface is provided with a ferromagnetic collection structure, such as plurality of ferromagnetic lines supported on an optically transparent surface.
Once the magnetically labeled biological entities are pulled sufficiently close to the surface by the externally applied gradient, they come under the influence of an intense local gradient produced by the ferromagnetic collection structure and are immobilized at positions laterally adjacent thereto. The local gradient preferably exceeds adhesion forces which can hold the biological entities to the transparent surface after they collide with the surface. Alternatively, the adhesiveness of the surface must be sufficiently weak to allow the horizontal magnetic force to move the magnetically labeled biological entities towards the ferromagnetic structures. The smoothness and the hydrophobic or hydrophilic nature of the surface are factors that can influence the material chosen for the collection surface or the treatment of this surface to obtain a slippery surface.
In accordance with the present invention, there are described further alternative embodiments and improvements for the collection chamber, the interior geometry of the collection chamber, and further useful techniques that may be accomplished by use of a vertical magnetic gradient separator structure.